1. Field of the Invention
The present invention relates to a light source apparatus and a head-up display apparatus incorporating the light source apparatus.
2. Description of the Related Art
Conventional automobiles and aircraft incorporate a head-up display (HUD) that displays display information received from various measuring instruments such as a speedometer or a fuel meter, map information for a navigation apparatus, and image information captured by an image-capturing apparatus.
For example, an on-vehicle head-up display apparatus includes a light source, a liquid crystal display (LCD) panel, a dichroic mirror, and a hologram mirror, which are installed behind an instrument panel of a vehicle. The various items of information displayed on a liquid crystal display panel are reflected by the dichroic mirror and hologram mirror, thereby projecting the optical information on a part of the window of the vehicle or on a reflective layer disposed at a position forward of the driver. In this manner, various items of information may be displayed as a virtual image, allowing the driver to visually recognize the formation without redirecting his or her line of sight.
Also, a head-up display has been proposed which employs an organic electroluminescence (EL) panel or a light emitting panel in which organic electroluminescence elements are arranged in a matrix of columns and rows (see Japanese Patent Application Laid-Open No. H11-67448). The organic EL elements of the organic EL panel are driven to emit light in accordance with video data information. Thus, the head-up display employing the organic EL elements has high intensity, not requiring a separate light source. In addition, the head-up display may be of simple, lightweight construction, thus lending itself to miniaturization. The organic EL panel includes a thin film constituted of a dielectric mirror, a clear electrode, a hole transport layer, a light emitting layer, and metal electrodes, aligned in this order on a glass substrate. Another glass substrate is placed on the thin film so that the thin film is sandwiched between the two glass substrates and is sealed from the environment by using a UV curable resin.
Since organic EL elements emit light by itself, a conventional head-up display apparatus does not require a separate light source. In order to display information on a reflective layer, the organic EL panel is required to display the information at high intensity. Unfortunately, the organic EL elements usually lose their intensity in a short time if high voltage is applied to them or large current flows through them.
In addition, an organic EL panel has a thin film sandwiched between two glass substrates and is sealed with resin. Thus, the panel is mounted to a head-up display apparatus with the glass surface directly bonded to the chassis of the head-up display for securely mounting the panel, or bonded to a bracket which in turn is fixed to the chassis of the apparatus. However, the bonded surface areas of the glass substrate are sensitive to impact or shock, and therefore the organic EL panel is often damaged before it is fixed to the chassis.